1. Field of the Invention
This invention relates to the field of froth flotation of clay such as kaolin containing mineral impurities such as titanium dioxide and more specifically relates to an apparatus and method for conditioning an aqueous pulp of clay particles and mineral impurities preparatory to subjecting the pulp to froth flotation.
2. Prior Art
It is customary, when clay is subjected to froth flotation, to first condition a slurry of the clay by adding to it activators such as calcium chloride and calcium oxide and oleic acid and subjecting the resulting mixture to very severe agitation so as to impart to the slurry an input of a substantial amount of horsepower hours, i.e. at least twenty-five horsepower hours of energy per ton of clay solids. It is believed that the titanium dioxide mineral impurity contains hydroxyl groups which, after a sufficient energy input, react with the calcium ion introduced by the above-mentioned activators to satisfy one of the valences of the calcium ion, the other valence being satisfied by reaction with the oleic acid anion to chemically bond the oleic acid molecule, i.e. the oleate to the titanium dioxide mineral impurity particle. The oleate renders the particle hydrophobic and more compatible with air bubbles which are subsequently introduced during the froth flotation phase of the process. It is furthermore believed that violent or prolonged agitation promotes the reaction of calcium ion with the titanium dioxide particle followed by reaction with the oleic acid.
Heretofore, in many cases conditioning was caused to take place within the flotation vessel prior to subjecting the pulp to froth flotation. U.S. Pat. Nos. 1,285,061, 3,437,203 and No. 3,491,880 illustrate a flotation apparatus but fail to disclose or suggest a plurality of generally horizontal baffles having holes in which a plurality of impellers are rotated by a common drive shaft. The impellers employed in the apparatus of these patents are used for the purpose of not only agitating but also sucking air into the pulp.
U.S. Pat. Nos. 3,864,438 and 3,872,010 also disclose flotation machines which, however, utilize a double blade impeller which cooperates with a set of circularly disposed vanes. Neither of these patents discloses or suggests the use of a plurality of impellers positioned and adapted to rotate on a common shaft in holes provided in a plurality of generally horizontal baffles.
A disadvantage of the prior art processes of froth flotation to remove titanium impurities from kaolin type clays has been the use of relatively large amounts of reagents compared to those amounts used in the flotation process in which the conditioning device of this invention is used. A further disadvantage of the prior art is the necessity of adding the reagents in stages interspersed by extended periods of conditioning. The reagent dosage, method of addition and high energy input of the prior art was necessitated by the inefficient application of energy to the very fine particles of clay such that an insignificant amount of the titanium impurity is scrubbed off the clay particles and made available for extraction from the water suspension in the froth flotation process. As a result of this deficient conditioning, costly reagents are used in an excess amount and the suspension must be greatly diluted (to less than 20% by weight and as low as 5% by weight) to effect the thorough removal of these reagents, their reaction products, and the titanium mineral impurity. The very dilute suspension which emerges from the froth flotation process must then be dewatered to useful commercial concentrations. Dewatering equipment for such fine particle clays is quite expensive, both to purchase and operate. In sum, the deficient conditioning results in a significantly and unnecessarily higher cost for reagents, conditioning and dewatering.